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    Pittsburgh Knee Rules

    Defines when knee x-rays are unnecessary, based on the Pittsburgh rules.
    When to Use
    Why Use

    The Pittsburgh decision rules can be applied to all patients with an acute knee injury in the past 1 week old, without prior knee surgery or ED evaluation.

    • The Pittsburgh knee rules were derived to aid in the efficient use of radiography in acute knee injuries.
    • Found in most studies to have a higher specificity than the Ottawa Knee Rule, which would mean fewer x-rays would be needed, while maintaining a sensitivity close to 100%.
    • Not useful in children under age 12 as all these patients would require x-rays by the Pittsburgh decision rules.
    • The Pittsburgh decision rules are not as well validated as the Ottawa Knee Rule with fewer external validation studies.
    • Patients without criteria for imaging by the Pittsburgh decision rules are highly unlikely to have a fracture and do not need plain radiographs.
    • It has a higher specificity than the Ottawa Knee Rule, reducing the number of false positives.
    • Application of the Pittsburgh decision rules can cut down on the number of unnecessary radiographs by up to 78%.


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    Next Steps
    Creator Insights


    Patients who do not meet the Pittsburgh decision rules do not need an x-ray. If one of the conditions are met, then x-ray is recommended.


    For significant non-bony injuries, often crutches and a knee immobilizer can be helpful to assist with ambulation.

    Critical Actions

    Patients who do not meet the Pittsburgh decision rules do not need an x-ray. If one of the conditions are met, then x-ray is recommended.


    Series of Yes/No questions, see below:

    Facts & Figures

    Criteria Response
    Mechanism Blunt Trauma or Fall Y/N
    Age < 12 Y/N
    Age > 50 Y/N
    Unable to bear weight in ED? (4 steps, limping is allowed) Y/N

    Evidence Appraisal

    • Original study was published in 1994 and consisted of a retrospective chart review followed by a prospective validation study. The authors reviewed all patients who presented to the ED with an acute knee injury during a 10 month period, excluding those patients who had injuries more than 1 week old, had isolated skin injuries, prior knee surgery, or were returning for re-evaluation. They analyzed 11 clinical variables on 201 patients with knee injuries, 12 (6%) of whom had a fracture on x-ray. From this, they found that combining a fall or blunt trauma mechanism with inability to ambulate or age < 12 or greater > 50 yielded a sensitivity of 100% and specificity of 63%. They prospectively applied these rules to 133 patients and had a sensitivity of 100% and a specificity of 79%. Would have led to reduction in x-ray usage by 78%.
    • Decision rule was prospectively externally validated and compared to the Ottawa Knee Rule in 1998. 745 patients with 91 fractures (12.2%) met the Pittsburgh inclusion criteria and yielded a sensitivity of 99%, specificity of 60% while the Ottawa inclusion criteria were met by 750 patients with 87 fractures (11.6%) with a sensitivity of 97% and specificity of 27%.
    • A study in 2005 utilized the Pittsburgh decision rule with triage nurses and physicians. 152 subjects were prospectively enrolled in the study with 13 fractures identified (8.6%). All patients enrolled in the study got an x-ray. The Pittsburgh decision rule would have missed four of 13 fractures with a sensitivity of 77% and specificity 57%. However, one of those fractures was found only on MRI while two others were avulsion or patellar fractures of low clinical significance.
    • Another study done in the Netherlands in 2013 comparing the Ottawa knee and Pittsburgh decision rules found that while both had a sensitivity of 86%, the Pittsburgh decision rule had a higher specificity of 51% while the Ottawa Knee Rule specificity was 27%.
    David Seaberg, MD

    From the Creator

    Why did you develop the Pittsburgh Knee Rules? Was there a clinical experience that inspired you to create these rules for clinicians?
    Back in the early 1990's, clinical decision rule research was just beginning. I found the Ottawa Ankle Rules to be a fascinating research and as a Chief Resident in Emergency Medicine at the University of Pittsburgh, I thought that a knee rule would also be useful. Since this type of research was fairly new to emergency medicine, I derived our rule from retrospective data and then prospectively validated it.
    What pearls, pitfalls and/or tips do you have for users of the Pittsburgh Knee Rules? Are there cases when they have been applied, interpreted, or used inappropriately?
    The beauty of the Pittsburgh Knee Rule is that it is fairly simple to use. I have heard some Orthopedic surgeons do not like the rule since it does not utilize more physical exam findings. The rule simply uses age and the ability to ambulate for 4 full weight-bearing steps on a flat foot. This exam finding is different than the Ottawa Knee Rule, which just requires any weight transfer onto the foot. The inter-rater reliability of the full weight-weight bearing steps has been found to be equally high.
    What recommendations do you have for health care providers once they have applied the Pittsburgh Knee Rules besides imaging, or when imaging is negative?
    As in any Clinical Decision Rule, the provider must explain the rule to the patient and that it rarely misses fractures. For an Emergency Physician, it is often just easier to order an x-ray (or order it from triage) rather than taking the time to explain the rule. However, there are times, after I explain the rule and try to convince the patient they do not need an X-ray, if the patient still requests an x-ray, I still order it. In the future, as value-based care and bundled payments become more prevalent, these type of evidence-based rules will become more important.
    What is your criteria to determine full weight bearing steps, as required in your algorithm?
    Four full weight-bearing steps on a flat foot

    About the Creator

    David Seaberg, MD, CPE, FACEP, is a professor and dean of the University of Tennessee College of Medicine, Chattanooga and a practicing emergency physician. He is also Senior Vice President of the Erlanger Health System. Previously, he was the residency director and chair of the Department of Emergency Medicine at the University of Florida and served as president and chairman of the Board of the American College of Emergency Physicians. Dr. Seaberg has over 130 publications, book chapters and abstracts and has received numerous teaching and research awards.

    To view David Seaberg, MD's publications, visit PubMed

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    About the Creator
    David Seaberg, MD
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